The recently discovered traces of ricin in a makeshift laboratory in a flat in London have caused a media frenzy over its potential use in a terrorist attack. Ricin was most famously used in the assassination of the Bulgarian dissident Georgi Markov when a platinum ball containing the poison was injected into his leg from the tip of an umbrella. He died three days later on 10 September 1978. The ricin-firing umbrella was developed by the Soviet secret police and was used to kill at least three other Bulgarian defectors and an attempted assassination of a fourth, again in London. Ricin itself is made from a naturally occurring protein produced by the castor bean plant and the way that it exerts its toxic action in the body is a story of subterfuge and deception to rival the Cold War umbrella assassinations.
The ricin molecule contains two main parts; one acts as the weapon, the other as a disguise.
The weaponry consists of a protein molecule whose job it is to prevent other proteins from being made. A protein is just a large natural molecule which has a particular job to do in the body (e.g. hemoglobin is a protein whose job it is to carry oxygen around the body) and the instructions for making these proteins are contained within our DNA. Ricin sabotages the machinery within the body that turns the instructions in DNA into functioning proteins. Without these proteins cells cannot function and die. As a result the organs in the body that are exposed to ricin start to fail. If ingested (eaten), ricin causes severe gastroenteritis and hemorrhaging followed by failure of the liver, spleen and kidneys. If breathed in, the symptoms include weakness, fever, cough, pulmonary oedema (fluid collecting in the lungs) and respiratory distress. In severe cases exposure to ricin can cause death.
The body is not without defences and one of the simplest is just to deny entry of toxins into our cells in the first place, but that is where the disguise comes in. Each cell has to let some molecules in and out in order for it to work together with the cells around it. The second part of ricin is a disguise so that when the poison encounters a cell it goes to the door where molecules are let in and is recognized as a friend. Only when it has managed to gain entry into the cell does ricin discard its disguise and use its weaponary to sabotage the protein-making machinery.
Interestingly, ricin is toxic to the very plant that makes it, but the plant overcomes this toxicity by making ricin as one long molecule incorporating both disguise and weapon stuck together in such a way that the disguise can not be taken off. Only when the ricin is excreted are ties that bind the disguise to the weapon loosened to allow the toxin to perform its deadly deception.